1. Field of the Invention
The present invention relates generally to liquid crystal display devices and, more particularly to the structure of a liquid crystal display device of the partial transmission and partial reflection type having both a transmissive display region and reflective display region.
2. Description of the Related Art
Owing to unique features such as thin or slim size, light weight and low power consumption, liquid crystal display devices are becoming more widely used as display devices for display of image and character information in a variety of types of electronic equipment including but not limited to information equipment such as personal computers, portable information terminals, mobile wireless telephone handsets, and visual equipment such as digital cameras and camera-embedded VTR apparatus and others. In recent years, in accordance with noticeable rapid popularization of mobile telephone handsets and handheld information terminals, demands for middle or small size liquid crystal display devices with extra-low power consumption are becoming strong more and more.
Traditionally, for liquid crystal display devices adaptable for use in personal computers and liquid crystal monitors, a transmissive display mode is generally used for controlling a transmission amount of light as emitted from a back-light unit by a liquid crystal panel. However, electrical power being consumed by the backlight is ordinarily more than 50% of total power consumed by the liquid crystal panel, and is impermissible for small size equipment such as portable telephones, mobile information terminals or the like. Due to this, these devices are designed to employ reflection-mode liquid crystal display devices which eliminate use of the backlight and which include a reflective plate as provided at a panel surface for permitting reflection of ambient light rays to thereby visually display images.
These liquid crystal display device of the reflection type are faced with a problem as to a decrease in on-screen image viewability in cases where ambient light is dark. In the case of certain equipment such as portable telephones being subject to both outdoor use and indoor use, ambient light-independent usability is required. A liquid crystal display device for solving such problem is disclosed in JP-A-2000-19563, which device comes with a transmissive display region and a reflective display region within a single picture element or “pixel” to thereby simultaneously realize both a transmissive display function and a reflective display function.
In addition, as methodology for improvement of the viewability during reflective displaying, a method is disclosed in JP-A-2000-162637, wherein an organic resin film with formation of a convexo-concave configuration having a circular planar shape and moderate cross-sectional shape is disposed on a surface beneath a reflective electrode layer for scattering or dispersing reflected light into an appropriate direction(s).
The related art liquid crystal display devices of the partial transmission/reflection or “transflective” type are encountered with problems inherent thereto, including an occasional decrease in respective aperture ratios of reflective part and transmissive part as compared to display devices of complete reflection type and complete transmission type. Due to this, it is very important to enhance the total aperture ratio of a combination of the reflective and transmissive parts in order to achieve the required brightness or luminance of display images. Since pixel aperture ratios are significantly variable depending upon the planar layout of wiring lead electrodes and reflective electrode plus pixel electrodes, such design is important; however, no discussions on this point are found in the related art.
Alternatively in standard liquid crystal display devices of the active matrix type, a charge storage capacitance is customarily provided at each pixel in order to suppress interelectrode parasitic capacitance components and/or pixel voltage variations otherwise occurring due to transistor leakage currents to thereby obtain excellent display quality. While the significance and layout of such storage capacitance appreciably affects the resultant pixel aperture ratios, no teachings are involved in the related art as to how the charge storage capacitance is to be provided in partial transmissive/reflective pixels.
Also note that in order to fabricate the intended convexo-concave configuration having moderate sectional shapes by use of organic resin material, it should be required to add one or more extra process steps to prior known TFT fabrication processes, resulting in an unwanted increase in manufacturing costs.